Frequency group separation filter device using laminated dielectric slab-shaped elements

ABSTRACT

A frequency group separation filer device using slab-shaped dielectric elements, preferably disposed in a beam-forming region defined between an antenna and feeder, the filter being so designed as to separate in reception the composed beams of high and low frequency groups respectively comprised of frequency components within a frequency region higher than or included in the microwave region into the individual original high and low frequency groups, and conversely in transmission to compose the separate beams of such high and low frequency groups. The branching filter comprises an assembly of a plurality of laminated plate dielectric elements each having a thickness equal to substantially one-fourth the wavelength of the central frequency of at least the aforesaid high frequency group and as a whole possessing at least two different dielectric constants. The filter further includes at least one further dielectric element having a thickness of about one-fourth the wavelength of the substantially central frequency of the low frequency groups disposed at at least one of the forward and rear sides of the assembly of laminated dielectric elements.

lii-l0-72 GR [451 Oct. 10, 1972 FREQUENCY GROUP SEPARATION FILTER DEVICE USING LAMINATED DIELECTRIC SLAB-SHAPED ELEMENTS Inventorsz Masaki Koyama, Saitama-ken; Sadakuni Shimada; Masahiro 'Karikomi, both of Tokyo, all of Japan Assignee: Nippon Telegraph and Telephone Public Corporation, Tokyo, Japan Filed: Nov. 5, 1970 Appl. No.: 87,278

Foreign Application Priority Data Nov. 11, 1969 Japan ..44/89764 June 11, 1970 Japan ..45/49997 US. Cl. ..343/909, 343/779, 343/781, 333/70 S Int. Cl. ..H0lq 15/02 Field of Search ..343/753, 755, 756, 779, 781, 343/909, 911; 333/70 S References Cited UNITED STATES PATENTS 7/1970 Schell ..343/909 4/1953 Southworth ..343/755 l/l954 Marie ..343/909 4/1957 Ramsay et al. ..343/909 FOREIGN PATENTS OR APPLICATIONS 562,602 3/1954 Canada ..343/756 Primary Exaininer-Eli Lieberman Attorney-Flynn & Frishauf [5 7] ABSTRACT A frequency group separation filer device using slabshaped dielectric elements, preferably disposed in a beam-forming region defined between an antenna and feeder, the filter being so designed as to separate in reception the composed beams of high and low frequency groups respectively comprised of frequency components within a frequency region higher than or included in the microwave region into the individual original high and low frequency groups, and conversely in transmission to compose the separate. beams of such high and low frequency groups. The branching filter comprises an assembly of a plurality of laminated plate dielectric elements each having a thickness equal to substantially one-fourth the wavelength of the central frequency of at least the aforesaid high frequency group and as a whole possessing at least two different dielectric constants. The filter further includes at least one further dielectric element having a thickness of about one-fourth the wavelength of the substantially central frequency of the low frequency groups disposed at at least one of the forward and rear sides of the assembly of laminated dielectric elements.

13 Claims, 17 Drawing Figures PATENTEDum 10 m2 SHEET 1 OF 7 FIG. 1

FIG. 2

PRIOR ART FIG. 3

' PRIOR ART FIG.4

PRIOR ART 35 1 .m m FD.

PATENIEBIHII w 1 2 3.698.001

SHEEI 2 OF 7 PATENTEDntI 10 m2 SHEU 5 OF 7 FIG. 16

FIG. 15

FREQUENCY GROUP SEPARATION FILTER DEVICE USING LAMINATED DIELECTRIC SLAB- SHAPED ELEMENTS tiplex telephony communication system utilizing an ar- 15 tificial satellite repeater.

A frequency group separation filter used in an antenna branching arrangement included in a wireless telecommunication apparatus applicable in common to 2 the aforementioned frequency regions should have a function of separating the both frequency groups from each other during reception, and composing the groups into a single signal during transmission, in order to use an antenna mechanism in common to said frequency groups. Throughout this specification the terms separating and branching are used substantially synonomously.

FIG. 1 is a schematic longitudinal sectional view of the prior art Cassegrain antenna assembly provided with the aforementioned function of the feeding (i.e., composing) and branching-off (i.e., separating frequency groups). Said Cassegrain antenna assembly consists of a frequency group separation filter 15 including a main reflector l1, sub-reflector 12, primary section 13, branching-off (i.e., separating) and feeding (i.e., composing) waveguide section 14 for signals and a pair of waveguides 16 and 17.

In transmission, the frequency group separation filter 15 composes signal components of a high frequency group and signal components of a low frequency group separately supplied through the waveguides l6 and 17, conducts the composed signals to the aforesaid feeding waveguide section 14 and radiates them through the air from the Cassegrain antenna mechanism 10 in the form of prescribed electromagnetic waves through the primary section 13, sub-reflector 12 and main reflector 11 in turn. Conversely upon reception, said branching (i.e., separating) filter receives already spatially radiated electromagnetic waves at the main reflector 11 and branches off the signals received through the sub-reflector 12, primary section 13 and aforesaid branching waveguide section 14 in turn into the original high and low frequency group signal components and conducts said separated signal components to the waveguides l6 and 17 respectively.

FIG. 2 is an enlarged longitudinal sectional view of said prior art frequency group branching filter 15. FIG. 3 is a cross sectional view on line 33 of FIG. 2 as viewed in the direction of the arrow. Upon reception, high frequency group signal components included in the signals supplied to the branching filter 15 pass through the slots 22 defined by a plurality of ducts connecting both waveguides 16 and 17 which are provided on their mutually facing walls at a substantially equal interval in the longitudinal direction of said waveguides and enter the waveguide 16. On the other hand, low

frequency group signal components move straight toward the waveguide 17. In transmission, the high and low frequency signal components travel in the reverse directions.

FIG. 4 is a longitudinal sectional view of another embodiment of the conventional frequency group branching filter. Upon reception, high frequency group signal components included in the signals supplied to the branching filter 31 in the direction of the arrow 32 advance toward a waveguide 33, while low frequency group signal components are reflected by a tapered wall section 34 and introduced into a branched waveguide 36 provided with a lowpass filter 35.

With the conventional frequency group branching filter 15 arranged as shown in FIGS. 1 to 3, the higher the frequency of transmitted signals, the smaller and more slots 22 have to be formed. Further, with a frequency group branching filter 31 constructed as il- 0 lustrated in FIG. 4, the branched waveguide 36 should be provided with a lowpass filter 35 so as to prevent signal components of the high frequency group from passing through the waveguide 36. In either case of the prior art device, the design and manufacture are extremely difficult. Moreover, the required formation of slots (FIGS. 1 to 3) or tapered walls (FIG. 4) in the waveguide most likely causes undesired high-order modes of the original high frequency group to be generated at the aforesaid sections. The occurrence of signal components of such undesired high-order modes of the original high frequency group leads to not only a degradation of the quality of transmitted signals, but also tracking errors, for example, in receiving electromagnetic waves from an artificial satellite repeater using such an antenna mechanism as shown in FIG. 1. Further, disadvantages of the conventional frequency group branching filter using the aforesaid types of waveguide are that when signals travel along the walls of the waveguide, there occurs heat loss, naturally imposing limitations on the maximum electrical energy to be handled and the frequency region of signals to be transmitted. Particularly in transmission through a single waveguide, it is difficult to raise the ratio of the highest to the lowest frequency to more than 2.

Therefore, in the field of a telecommunication system used in common to high and low frequency regions, by means of, for example, a satellite repeater, there has in recent years suddenly grown a strong demand for the realization of a branching filter the loss of which is extremely low for signals during transit through a waveguide and can also handle a greater maximum electrical energy and an increased frequency band of transmitted signals.

FIG. 5 is a perspective view of a typical example of the aforesaid branching filter. This filter is prepared by juxtaposing a plurality of dielectric plates or slabs 4; to 4, with the adjacent major planes facing each other with a substantially equal spacing therebetween, which are each formed with a thickness equal to substantially one-fourth the wavelength of the central frequency of the higher frequency group included in the original signal and have substantially the same or different dielectric constants.

When incident waves A including those having broad frequency components consisting of electromagnetic waves to be selected are brought into a branching filter 40 of the aforesaid construction along or at a proper angle of inclination to the arrangement of the dielectric plates 4, to 4,,, then signal components included in said frequency region to be selected are concentratedly obtained in the form of reflected waves B and the remaining frequency components included in other frequency regions are derived in the form of transmitted waves C Accordingly, it will be understood that said branching filter is well adapted to be used as a kind of filter for signals to be selected.

Further, a filter using the above-mentioned dielectric plates is not only simpler in design and lower in manufacturing cost, but also the transmission loss is decreased because of its applicability in the free space, in comparison with a filter using a waveguide. Further, the generation of signal components having undesired higher-order modes of the original high frequency group is prevented, so that the filter can be expected to handle a greater maximum electrical energy and signals having a broader frequency band.

However, a branching filter using such dielectric plates already put to practical application is capable of selecting signal components only having a single frequency band. There has not yet been realized the socalled or separating frequency group branching filter capable of separately detecting signal components having as broad a frequency range as two or more bands particularly in that area of a free space through which there are transmitted beams.

Where it is desired to use a branching filter consisting of the aforementioned dielectric plates in a lower frequency region than that of microwaves, said dielectric plates will have to become exceedingly thick in order fully to display a filtering property, so that such filter is in fact only applicable to signals having frequency regions higher than, or the same as, those of microwaves.

The present invention has been accomplished in view of the aforesaid situation and is intended to provide a frequency group branching or separating filter device wherein there is disposed in a beam-forming region defined between an antenna and feeder a frequency group branching filter prepared from dielectric elements capable of branching off and composing the beams of two frequency groups consisting of signal components within a frequency region higher than or included in the microwave region.

Therefore it is an object of the present invention to provide a frequency group branching filter device capable of reducing transmission loss more effectively and handling signals having a broader frequency band than has been possible with the conventional type of filter using a waveguide. Another object of the invention is to provide a frequency group branching filter device which, due to its applicability in free space, prevents the generation of undesired higher-order modes of the original high frequency group and in consequence the occurrence of errors in tracking a satellite repeater and further increases a maximum energy to be handled. A further object of the invention is to provide a frequency group branching filter device which permits far easier mechanical design and manufacture and consequently offers much greater economic advantage than the type using a waveguide. A still further object of the invention is to provide a frequency group branching filter device which eliminates the necessity of providing a phase shifter operable over a superbroad frequency band, said phase shifter being indispensable, though practically unrealizable, for a waveguide type branching filter, into which, in satellite telecommunication, there are introduced incident electromagnetic waves at indefinite angles of inclination to its wavereceiving plane.

SUMMARY OF THE INVENTION According to an aspect of the present invention, there is provided a frequency group separating filter device so designed as to separate in reception of the composed beams of high and low frequency groups including of signal components respectively within a frequency region higher than or included in the microwave region and conversely in transmission to compose beams of high and low frequency groups, said filter comprising an assembly of a plurality of laminated plate dielectric elements each having a thickness equal to substantially one-fourth the wavelength of the substantially central frequency of at least said high frequency group and as a whole possessing at least two different dielectric constants. The filter further includes at least one further dielectric element having a thickness of about one-fourth the wavelength of the substantially central frequency of the low frequency groups disposed at at least one of the forward and rear sides of the assembly of laminated dielectric elements.

The present invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic longitudinal sectional view of the conventional Cassegrain antenna assembly provided with a frequency group branching or separating filter;

FIG. 2 is a fragmental enlarged longitudinal sectional view of the frequency group branching filter of FIG. 1;

FIG. 3 is a cross sectional view on line 3-3 of FIG. 2 as viewed in the direction of the arrow;

FIG. 4 is a longitudinal sectional view of another embodiment of the conventional frequency group branching filter;

FIG. 5 is a perspective view of a typical example of the conventional branching filter capable of reducing transmission loss of signals and handling signals having a broad frequency band;

FIG. 6 is a perspective view of a frequency group branching filter device using dielectric elements according to an embodiment of the present invention;

FIG. 7A is a perspective view showing the concrete construction of a frequency group branching filter according to an embodiment of the present invention;

FIG. 78 illustrates the action of the frequency group branching filter of FIG. 7A;

FIG. 8 is a perspective view showing the concrete construction of a frequency group branching filter according to another embodiment of the invention;

FIG. 9 is a graph illustrating the attenuation characteristics of the reflected and transmitted waves derived from transmission of incident beams through a frequency group branching filter of FIG. 8;

FIG. 10 is a graph illustrating the properties of various dielectric materials obtained by plotting the ratio a of the vertically polarized waves to the horizontally polarized waves on the abscissa and the reciprocals a of the specific dielectric constants of said materials on the ordinate, with the incident angle 0 defined by incident waves with the surface of the present frequency group branching filter taken as a parameter;

FIG. 11 is a perspective view of the concrete construction of a frequency group branching filter according to still another embodiment of the invention;

FIG. 12 is a perspective view of the concrete construction of a frequency group branching filter according to a further embodiment of the invention;

FIGS. 13 and 14 are graphs illustrating the attenuation characteristics of the reflected and transmitted waves of beams transmitted through the present frequency group branching filter constructed as shown in FIG. 12; FIG. 13 representing the case where the filter includes five dielectric elements excluding a matching layer and FIG. 14 the case where the filter includes nine dielectric elements excluding a matching layer;

FIG. 15 is a longitudinal sectional view of a frequency group branching filter device using dielectric elements according to a further embodiment of the invention; and

FIG. 16 is a longitudinal sectional view of a frequency group branching filter device using dielectric elements according to a still further embodiment of the invention.

There will now be described by reference to the appended drawings the preferred embodiments of a frequency group branching or separating filter device according to the present invention, showing for convenience of explanation, but not in the sense of limiting the scope of the invention, the case of applying said device to an antenna branching assembly used in satellite telecommunication in common to various frequency bands.

The occupied frequency region internationally recognized at present for satellite telecommunication includes a microwave region of 4 to 6 GHz. In the near future there will be taken into consideration a quasimillimeter wave region of 10 to 30 GHz.

Further in the long-range view, there will be contemplated the use of millimeter wave region of 40 to 100 GHz.

Let it be assumed to use the microwave region and the quasi-millimeter wave region as high and low frequency regions respectively, and that the filter device is to be used in space satellite telecommunication. Then the highest and lowest frequencies will bear the ratio of 30 GHz/4 GI-Iz 7.5. The conventional frequency group branching filter device using a waveguide would only permit said ratio to be about 2 at most and could hardly effect the branching-off and composition of both groups of frequencies by means of a single antenna assembly. The present invention is therefore intended to provide a frequency group branching filter device capable of branching-off and carrying out the composition of frequency components respectively included in the aforesaid two groups of frequency bands by means of a single antenna assembly.

FIG. 6 is a perspective view of such branching filter device according to an embodiment of the present invention. There is provided an antenna 53 consisting of,

for example, a main reflector 51 having a parabolic reflecting plane and a sub-reflector 52 so disposed as to have the same focal point as said main reflector S1 and having a hyperbolic reflecting plane.

A feeder 56 comprises a high frequency branching filter 54 and a low frequency branching filter 55, each of which is provided with a waveguide. Upon reception, these high and low frequency filters 54 and 55 are supplied with low and high frequency band signal components consisting of high and low frequency group beams f and f passing through the antenna 53 and preliminarily branched off by the later described frequency group branching filter of the present invention and further split said low and high frequency band signal components f and f,, into a plurality of smaller frequency band signal components f f andf f respectively, and in transmission perform a reverse operation.

The present invention resides in providing the undermentioned frequency group branching filter in a free space defined between the antenna 53 and feeder 56 so as to be used as a beam forming section.

FIG. 7A is a perspective view of the concrete construction of such frequency group branching filter. Let it be assumed that the high frequency group beam to be branched off consists of two frequency bands of 18 and 26 GI-Iz and the low frequency group beam to be transmitted is formed of two frequency bands of 4 and 6 GHz. That is, a pair of waves of the 4 and 18 GI-Iz bands are received and another pair of waves of the 6 and 26 GI-Iz bands are transmitted, or visa versa. Then a beam branching filter 57a of the present invention is prepared by laminating, for example, first to third dielectric elements 61, 62 and 63 each formed with a thickness equal to substantially one-fourth the wavelength of 23.5 GHz substantially constituting the central frequency of the high frequency group selected from the design standpoint, and the elements 61-63 having different dielectric constants.

When there are introduced, as shown in FIG. 7B, electromagnetic waves 64 consisting of a composite of the aforementioned high and low frequency group beams at a proper angle of inclination to the surface of either side plate of the laminate constituting said beam branching filter 57a, then the greater part of the high frequency group beam becomes a reflected wave 65 on the surface of a first dielectric element and the remainder is conducted as a transmitted(or permeated) wave 66. The transmitted wave 66 is next brought to a second dielectric element 62, on the surface of which the greater part of the high frequency group beam still included in said transmitted wave 66 becomes a reflected wave 67 and the remainder is further transmitted as a transmitted wave 68. This transmitted wave 68 is conducted to the third dielectric element 63 wherein there is repeated the same action as that of the first and second dielectric elements 61 and 62, that is, the greater part of the high frequency group beam still contained in the wave 68 permeated through the second dielectric element 62 is reflected from the surface of the third dielectric element 63 and the remainder is drawn outside as a transmitted wave 69. Of the incident waves 64, said beam branching filter causes most of the high frequency group beam to be reflected and most of the low frequency group beam to be transmitted.

When disposed, therefore, in the beam forming section between the antenna 53 and feeder 56 as shown in FIG. 6, the beam branching filter of the invention branches off upon reception the high frequency group beam consisting of f,,,, f as a reflected wave and the low frequency group beam consisting of f,,,, f as a transmitted wave, and in transmission performs an opposite action. To give a concrete example, frequency bands of 4 and 18 61-12 are received and those of 6 and 26 61-12 are transmitted or vice versa.

FIG. 9 is a graph of the attenuation of reflected wave I and transmitted wave 1 of a beam branching filter 57b prepared from five laminated dielectric elements 71 of glass disposed at a substantially equal spacing in a free space 72 illustrated in FIG. 8. As is well known, an increased number of laminated dielectric elements enables a broader frequency region to be effectively handled.

The inventors experiments to date show that a dielectric element usable as a frequency beam branching filter may consist of polystyrene (specific dielectric constants,'=:2.54), fused quartz (e,=.3.78), glass (e,=.7) and poly-2, S-dichlorostyrene (6, 123) and it is also possible to utilize a free space (e,'":l) for this purpose. Where said free space is employed as a sort of dielectric element, mere provision of dielectric elements of a different kind at a substantially equal interval will be sufficient to realize a beam branching filter substantially equivalent to that of FIG. 7.

Let us now consider the relationship of beams introduced into the aforesaid beam branching filter versus the resulting reflected and transmitted waves. Where the incident beams consist of, for example, vertically and horizontally polarized waves intersecting each other at right angles like electromagnetic waves or permissibly two independently polarized waves), then it is preferred that to obtain ideal reflected and transmitted waves with respect to both polarized waves, incident beams be introduced theoretically in a direction intersecting at right angles the surface of the plate dielectric elements constituting the beam branching filter the incident angle in this case is herein defined as zero). However, such a process would cause the reflected wave to be sent back in its incoming direction, failing to be used in such frequency group branching filters.

In practice, therefore, incident waves must be introduced at proper angle of inclination to the surface of plate dielectric elements constituting the beam branching filter.

FIG. 10 is a graph of the properties of various dielectric materials obtained by plotting the ratio a of the vertically polarized waves to the horizontally polarized waves on the abscissa and the reciprocals a of the specific dielectric constants e, of said materials on the ordinate, with the incident angle defined by incoming beams with the surface of the beam branching filter taken as a parameter. As seen from FIG. 10, the nearer the ratio a on the abscissa approaches 1, the better will be the reflected and transmitted waves derived from both polarized waves. The ratio A /A of of FIG. represents that which the cut-off wavelength A, (defined by an image parameter) of the reflected or transmitted wave bears with the wavelength corresponding to the central frequency designed (in this embodiment, 23.5 GHz). FIG. 10 means that the larger the ratio of It /A the broader frequency band can be handled by the beam branching filter.

As apparent from FIG. 10, the smaller the incident angle 0, the more excellent will be the properties displayed by the beam branching filter. Experiments show that it is preferred for practical application to set the incident angle 0 at less than about 30. FIG. 10 further indicates that the larger the specific dielectric constant e,- of a dielectric element used, the broader is the frequency band that can be handled by the beam branching filter.

It has been disclosed with respect to the aforesaid two independently polarized incident waves that the reflecting and transmitting properties of the beam branching filter can be improved depending on the arrangement of dielectric elements as well as on the magnitude of the incident angle 0 at which incident waves are made to enter said filter.

FIG. 11 is a perspective view of the concrete construction of such a frequency group branching filter. This filter is prepared by integrally laminating on both sides of a single plate dielectric element 81 made of a proper material a pair of other plate dielectric elements 82 of different material from that of the former element. In said paired plate dielectric elements 82 are further embedded a plurality of substantially ribbonshaped dielectric elements 83 made of still another material at with a substantially equal spacing therebetween. A beam branching filter 57c of such construction has two groups of dielectric elements disposed in two dimensions, that is, in the direction in which there are introduced incident waves 64 as well as in a direction intersecting the former at substantially right angles, for example, so that one group of dielectric elements effectively acts on one of the aforesaid independently polarized waves and the other group also effectively handles the other polarized incident waves. Accordingly, said beam branching filter 570 can display better reflecting and transmitting properties with respect to said independently polarized waves.

As is apparent from FIG. 9, with a beam branching filter constructed as shown in FIGS. 7 and 8, the low frequency group beam obtained as a transmitted wave presents such attenuation characteristics that there occurs a wavy appearance over the broad frequency range of said low frequency group beam. Except for a certain narrow frequency region, said attenuation is unsatisfactory, preventing the beam branching filter from fully displaying its function. To speak concretely in connection with FIG. 9, a maximum reflected component of incident beams having a frequency of 4 to 6 GHz indicates a level of 5 dB, resulting in the loss of a transmitted wave by that extent. Obviously such a beam branching filter will fail to perform its function properly.

FIG. 12 is a perspective view of the concrete construction of a frequency group beam branching filter 57d according to the present invention so designed as to eliminate the aforesaid wavy appearance during attenuation of the low frequency group beam. This filter 57d is prepared by arranging, for example, on both the forward and rear sides of an assembly 57b of laminated dielectric elements fabricated in the same manner as in FIG. 8, two groups of dielectric elements 91 and 92 so as to match, for example, two different low frequency groups, each of the latter group of dielectric elements 91 and 92 being formed with a thickness substantially equal to one-fourth the wavelength of the substantially central frequency (in this embodiment, about 5 GI-Iz) of the low frequency group beam f With a beam branching filter 57d of the aforesaid construction, the dielectric elements 91 and 92 act as an impedance transformer so as to match the impedance of the free space with the input impedance of the assembly of laminated dielectric elements 57b with respect to the low frequency group beam f,,. The arrangement of FIG. 12 better eliminates the wavy appearance accompanying the attenuation of a transmitted wave than in the case where said dielectric elements 91 and 92 are not provided.

FIGS. 13 and 14 are graphs of the attenuation characteristics of waves reflected and transmitted by the beam branching filter 57d of FIG. 12; FIG. 13 representing the case where the filter consists of five dielectric elements including three glass plates (e,.=.7) and two intervening free spaces (e,.'-.1) excluding a matching layer, and FIG. 14 the case where the filter is prepared from nine dielectric elements including five glass plates and four intervening free spaces excluding a matching layer.

Now let us determine by a theoretical equation the ideal specific dielectric constants of e, and 6 demanded of said dielectric elements 91 and 92. With the normalized wave impedance of the assembly 57b of dielectric elements represented by Z, and the wavelength of the low frequency group beam by M, then the input impedance R of the laminated dielectric elements 57b with respect to the low frequency group beam may be expressed as f cos where: if I where:

wP tan where:

(b a parameter indicating a frequency region centered about the low frequency group beam.

From-the above equations (1) and (2) are deter- FIG. 15 is a longitudinal cross section of a frequency group beam branching filter device using dielectric elements according to another embodiment of the present invention. In this embodiment, there is further provided between the antenna 53 and feeder 56 shown in FIG. 6 a single rotary parabolic reflector 101 through which the high and low frequency group beams are transmitted and received. This filter device has an effect of more easily varying the incident angle defined by incident waves with the surface of the beam branching filter 57.

FIG. 16 is a longitudinal sectional view of a frequency group beam branching filter device using dielectric elements according to still another embodiment of the present invention. In this embodiment, there are provided a pair of rotary parabolic reflectors 111 and 112 in such a manner as to face the receiving and transmitting surfaces of the high and low frequency group branching filters 54 and 55 constituting the feeder 56. There is further provided a plain reflector 13 in a manner to face, for example, one of said parabolic reflectors indicated by l 12.

A beam branching filter of such arrangement can more freely control the incident angle defined by incident waves with the surface of said filter and over a broader range than the embodiment of FIG. 15, and moreover offers the advantage of allowing, as illustrated in FIG. 16, the high and low frequency group beam branching filters 54 and 55 to be arranged on the same plane.

What we claim is:

l. A frequency group separation filter device for separating, in signal reception, composed electromagnetic beams of high and low frequency groups respectively including frequency components within a frequency region higher than or included in the microwave region, said filter composing in signal transmission separate electromagnetic beams of high and low frequency groups respectively including frequency components within a frequency region higher than or included in the microwave region, said filter comprisan assembly of a plurality of laminated slab-shaped dielectric elements, each having a thickness equal to substantially one-fourth the wavelength of the substantially central frequency of said high frequency groups, and said dielectric elements respectively exhibiting at least two different dielectric constants; and

at least one further dielectric slab-shaped element having a thickness equal to substantially one fourth the wavelength of the substantially central frequency of the low frequency groups disposed at at least one of the forward and rear sides of said assembly of laminated dielectric elements.

2. A filter device according to claim 1 including at least two further dielectric elements respectively disposed at the forward and rear sides of said laminated assembly.

3. A filter device according to claim 1 wherein said at least one further dielectric element isso formed and located to satisfy the following equation for the input impedance R of the laminated assembly, the normalized wave impedance of the laminated assembly being givenas Z:

where:

l thickness of the respective laminated dielectric slabs;

XL wavelength of the electromagnetic waves of the low frequency groups; and

17 incident angle defined by incident electromagnetic wave with the surface of said filter device.

4. A filter device according to claim 1 wherein said high and low frequency groups separated in reception are different from said high and low frequency groups composed in transmission.

5. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is formed by a free space.

6. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is formed of polystyrene.

7. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is made of fused quartz.

8. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is glass.

9. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is made of poly-2, 5-dichlorostyrene.

10. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly includes a plurality of other dielectric elements embedded therein at a substantially equal inter val.

11. A filter device according to claim 1 wherein the electromagnetic beams of high and low frequency groups to be separated and composed by said filter have frequency regions of 17 to 30 and 4 to 6 GHZ respectively.

12. A filter device according to claim 1 wherein the electromagnetic beam of at least one of the high and low frequency groups is split into a plurality of smaller frequency divisions.

13. A filter device according to claim 1 wherein the incident angle at which incident electromagnetic bearns enter said filter is less than about 30. 

1. A frequency group separation filter device for separating, in signal reception, composed electromagnetic beams of high and low frequency groups respectively including frequency components within a frequency region higher than or included in the microwave region, said filter composing in signal transmission separate electromagnetic beams of high and low frequency groups respectively including frequency components within a frequency region higher than or included in the microwave region, said filter comprising: an assembly of a plurality of laminated slab-shaped dielectric elements, each having a thickness equal to substantially onefourth the wavelength of the substantially central frequency of said high frequency groups, and said dielectric elements respectively exhibiting at least two different dielectric constants; and at least one further dielectric slab-shaped element having a thickness equal to substantially one-fourth the wavelength of the substantially central frequency of the low frequency groups disposed at at least one of the forward and rear sides of said assembly of laminated dielectric elements.
 2. A filter device according to claim 1 including at least two further dielectric elements respectively disposed at the forward and rear sides of said laminated assembly.
 3. A filter device according to claim 1 wherein said at least one further dielectric element is so formed and located to satisfy the following equation for the input impedance R of the laminated assembly, the normalized wave impedance of the laminated assembly being given as Z:
 4. A filter device according to claim 1 wherein said high and low frequency groups separated in reception are different from said high and low frequency groups composed in transmission.
 5. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is formed by a free space.
 6. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is formed of polystyrene.
 7. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is made of fused quartz.
 8. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is glass.
 9. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly is made of poly-2, 5-dichlorostyrene.
 10. A filter device according to claim 1 wherein at least one of the dielectric elements of said laminated assembly includes a plurality of other dielectric elements embedded tHerein at a substantially equal interval.
 11. A filter device according to claim 1 wherein the electromagnetic beams of high and low frequency groups to be separated and composed by said filter have frequency regions of 17 to 30 and 4 to 6 GHz respectively.
 12. A filter device according to claim 1 wherein the electromagnetic beam of at least one of the high and low frequency groups is split into a plurality of smaller frequency divisions.
 13. A filter device according to claim 1 wherein the incident angle at which incident electromagnetic beams enter said filter is less than about 30*. 